Conventional position measuring systems for determining the position of two parts movable relative to one another, for instance on a machine tool, are as a rule connected via a certain number of signal transmission lines with a downstream evaluating unit, for instance a numerical controller. In principle, in transmitting various signals between the position measuring system and the downstream evaluating unit, the attempt is made to keep the number of signal transmission lines required as low as possible. Besides avoiding unnecessary cable-laying effort and expense, another object in the transmission of possibly desired additional signals is to keep the compatibility with the previously conventional number of signal transmission lines assured as much as possible.
From European Patent Application EP 0 660 209 A1 of the present applicant, a position measuring system is known which includes among other elements a read/write memory unit. The memory unit is used in particular for storing system-specific parameters, which can be transferred to the position measuring system for instance from the downstream evaluating unit. When the memory unit is read out, in turn, certain system-specific parameters are transferred from the position measuring system to the evaluating unit. The system-specific parameters that can be stored in the memory unit and read out again are parameters of the entire system, for instance comprising an evaluating unit, a machine tool, and a position measuring system, if the corresponding position measuring system is used in a machine tool. Specifically, this may involve the specification of the measurement system type, the width of the signal period, specifications on the measurement steps in the position measuring system, the form of output signals furnished, reference signal information, machine tool parameters, correction values for the generated signals, and many more.
With the aid of such a memory unit in the position measuring system, it is now possible for instance prior to the actual measurement mode to program the position measuring system in a suitable way, by modifying certain parameters in the memory unit. On the other hand, the evaluating unit used can also be adapted to the existing overall system, by transferring certain parameters from the memory unit to the evaluating unit.
For bidirectional transmission of the system-specific parameters between the position measuring system and the downstream evaluating unit, a separate signal transmission line may for instance be provided. However, this increases the aforementioned cable-laying effort and expense, and moreover in that case the desired compatibility with previous interface standards no longer exists.
The object of the present invention is therefore, in position measuring systems having a read/write memory unit and with the provision for transmission of system-specific parameters from and to an evaluating unit, to keep the expense for the requisite signal connections as low as possible. In particular, given the possible transmission of such system-specific parameters, compatibility with previous interfaces is also desired.
The transmission of incremental position information over a supply line between a position measuring system and an evaluating unit is known from German Patent Disclosure DE 195 04 822. However, this reference neither discusses how system-specific parameters should be transmitted as reliably as possible nor provides details on designing a suitable apparatus or a corresponding method.